In open pit coal mines, open pit rock quarries, and other types of open pit mining operations, blasting is carried out to remove overburden covering an orebody, to break ore to allow it to be loaded and hauled away, and to break rock to allow it to be loaded and hauled away. The blasting part of these operations must be carried out to optimize the use of the availale explosive energy. This includes obtaining the desired breakage and throw of the ore and rock. While accomplishing the above, it is becoming increasingly important to minimize the effects of blasting on nearby structures such as homes, schools, offices, etc. One significant way in which such blasting can affect nearby structures is through the ground vibration produced by the blast.
Several methods are being used to minimize ground vibration and still obtain the desired blasting results. These generally involve minimizing the amount of explosives detonated at a given time by separating a shot into a number of small blasts that are individually detonated in time sequence. Some examples of these methods are:
A. The use of delay electric blasting caps. PA1 B. The use of nonelectric blasting caps. PA1 C. The use of decked charges (explosive charges in a borehole separated by an inert barrier). PA1 D. The use of detonating cord with delay connectors. PA1 E. The use of delay electric blasting caps in combination with a sequential blasting machine which effectively increases the number of available periods by delaying the shot firing between individual cap circuits.